Package including a lidstock laminate

ABSTRACT

A method of forming a package by heat sealing a trap-printed laminate to a support member (e.g., tray). The laminate has a free shrink in each of the transverse and machine directions of at least about 10% at 200° F. and at least about 21% at 240° F. The laminate has an oxygen transmission rate of no more than about 100 cubic centimeters. The outside layer of the laminate comprises at least about 40% of one or more relatively high-melt polymers each having a melting point at least about 25° F. higher than the lowest melting point polymer of the sealant layer. The first film has an oxygen transmission rate greater than the oxygen transmission rate of the second film.

BACKGROUND OF THE INVENTION

The present invention relates to a packaging film, and more particularlyto a laminate useful as a lidstock for sealing a tray closed.

It is common in food packaging operations for a food product, such asfresh meat, to be placed on a tray, such as a thermoformed expandedpolystyrene tray having a central depressed area and a surroundingperipheral flange. A thermoplastic film or laminate may then bepositioned over the food and heat sealed to the peripheral flange tohermetically enclose the food product. In such arrangement, thethermoplastic film or laminate is the “lid” or “lidstock” and the trayis a “support member.”

The lidstock should be capable of forming a strong, hermetic seal withthe support member. This is true even where the sealing area of the traymay be exposed or contaminated with by-product (e.g., meat purge) fromthe packaged food. This is also true where, as is commonly the case, thesupport member is relatively rigid. Heat sealing a flexible lidstock toa rigid support member is more challenging than heat sealing theflexible lidstock to either another flexible film or laminate or toitself (for example, in a fin seal arrangement commonly used in verticalform-fill-seal operations).

To heat seal the lid to the support member, a heated bar engages theoutside of the lid to compress it against the flange of the supportmember. In so doing, heat transfers from the heated bar to the outsideof the lid, through the thickness of the lid, to the inside sealantlayer of the lid, and to the flange of the support member. The resultingheat and compression causes the contacting surfaces of the lid andsupport member to become molten and to intermix with one another. Theheating bar is then removed to allow the sealed area to cool and form asealed bond.

The heat from the heat seal process may also cause a heat-shrinkablelidstock to shrink or create a shrink tension in the areas of thelidstock that have been exposed to a sufficient amount of heat for asufficient amount of time to effect a shrink.

The seal strength of the resulting sealed package may be determined byseveral methods. The support member may be pierced with an inflationneedle and the interior of the sealed package may then be inflated untilthe lid or seal between the lid and support member fails. A higherinternal inflation pressure at failure indicates a stronger sealstrength. Alternatively, the sealed package may be placed in a vacuumchamber and subjected to decreasing external pressures until failure—alower external pressure at failure indicating a stronger seal strength.Also, a representative sample of the seal may be cut from the sealedpackage (or formed separately) so that the lidstock may be pulled fromthe support member, for example, using an Instron tensile tester underspecified conditions. A higher maximum force attained before failureindicates a stronger seal strength.

In all of these tests of seal strength, the failure mechanism may occurin one or more of several ways. In each case, the failure mode seeks afailure path requiring the least amount of force. For example, the bondbetween the lidstock and the support member may fail adhesively so thatthe lidstock simply peels away from the support member. Or, the lidstockmay fail cohesively along a path cutting generally perpendicularlythrough one or more layers of the lidstock—and then fail adhesivelyalong the interface between two layers of the lidstock. The failure pathmay combine an intricate path of cohesive and adhesive failures—allwhile the lidstock is being stretched by the applied force—to present acomplicated failure mode.

The above discussion is made to establish that a weaker cohesivestrength within a layer of the lidstock and/or a weaker adhesive bondstrength between layers of the lidstock may weaken the seal strength ofthe sealed package. This is especially true where the seal strengthfailure mode is not simply the peeling of the lidstock from the supportmember by adhesive failure of the sealing bond between the lid and thesupport member.

A desirable lidstock provides gas (e.g., oxygen, carbon dioxide) barrierattributes sufficient to enhance the storage life of the packaged food.The barrier characteristics of the lidstock may have increasedimportance where the interior atmosphere of the package may be modified,for example, to decrease the concentration of oxygen from that ofambient air or to increase the concentration of oxygen and carbondioxide from that of ambient air. For example, in packaging meat, theatmosphere in the sealed package may comprise about 80% by volume oxygenand about 20% by volume carbon dioxide in order to inhibit the growth ofharmful microorganisms and extend the time period in which the meatretains its attractive red (“bloom”) coloration. Oxygen and carbondioxide barrier attributes may be imparted to a film by incorporating,for example as a film layer, one or more resins having low permeabilityto oxygen. (Since carbon dioxide barrier properties generally correlatewith oxygen barrier properties, only oxygen barrier properties arediscussed in detail herein.)

It is not unusual for the inter-layer bond strengths associated with theincorporation of barrier resins or barrier layers into a lidstock to beweaker than the inter-layer bond strengths that would be present if thebarrier resin or layer were absent. That is to say, the inter-layer bondstrength between a barrier layer and an adjacent layer is usually theweakest inter-layer bond strength of a film. It is also possible thatweaker inter-layer bond strengths may be associated with one or more“tie layers” that may accompany the use of a barrier layer. Although atie layer may be inserted between the barrier layer and an otherwiseadjacent film layer in order to improve the inter-layer bond adhesion,the resulting bond strength between the tie layer and its adjacent filmlayer may be less than the bond strength between the tie layer and itsadjacent barrier layer. Accordingly, the tie layer may present theweakest inter-layer bond strength of the lidstock—and thus present thefailure path during a seal strength test.

In order to produce packaged product at a fast (and thereforeeconomical) rate, the lidstock should be capable of being quickly heatsealed to the support member. A lidstock that facilitates quick heatsealing is said to have good “sealability.”

It is also desirable for the lidstock to be printed. Such printingprovides important information to the end-user of the packagedfood—information such as the ingredients of the packaged food, thenutritional content, package opening instructions, food handling andpreparation instructions, and food storage instructions. The printingmay also provide a pleasing image and/or trademark or other advertisinginformation to enhance the retail sale of the packaged product.

Such printed information may be placed on the outside surface of thelidstock. However, such surface printing is directly exposed to a heatedbar during the heat seal operation that seals the lid to the supportmember. As a result, the surface printing may become smeared orotherwise degraded. A surface printing is also exposed to other physicalabuses during distribution and display of the packaged product. Suchabuse may also degrade the clarity and presentation of the printedimage.

Once the lidstock has been sealed to a support member to form a closedpackage, it is also desirable that the lidstock not appear wrinkled orwavy. Such wrinkles or waves tend to form in the corner areas of asealed lidstock—and may appear even if the sealed lidstock forms atight, “drum-like” lid for the support member. The wrinkles may alsoappear as relatively small film corrugations near the sealed area of thelid, in particular at the leading and trailing ends (relative to themachine direction) of the package. Such wrinkles or waves cause thepackage to present a less than desirable appearance to the customer.

SUMMARY OF THE INVENTION

The present invention addresses one or more of the aforementionedproblems. A laminate is provided that comprises a first film having aninside surface and an outside surface opposite the inside surface of thefirst film. The first film comprises a sealant layer forming the insidesurface of the first film. The sealant layer comprises one or morepolymers each having a given melting point. At least one polymer of thesealant layer has the lowest melting point of the one or more polymersin the sealant layer. The laminate also comprises a second film havingan inside surface and an outside surface opposite the inside surface.The second film comprises an outside layer forming the outside surfaceof the second film. The outside layer comprises at least about 40% byweight of the outside layer of one or more relatively high-melt polymerseach having a melting point at least about 25° F. higher than the lowestmelting point polymer of the sealant layer. The laminate also includes aprinted image between the first and second films. The first film has anoxygen transmission rate greater than the oxygen transmission rate ofthe second film, measured (at standard temperature and pressure) persquare meter per day per 1 atmosphere of oxygen pressure differentialmeasured at 0% relative humidity and 23° C. The laminate has an oxygentransmission rate of no more than about 100 cubic centimeters (atstandard temperature and pressure) per square meter per day per 1atmosphere of oxygen pressure differential measured at 0% relativehumidity and 23° C. The laminate has a free shrink in each of thetransverse and machine directions of at least about 10% at 200° F. andat least about 21% at 240° F. The laminate is heat sealed to a supportmember to form a closed package.

Heat sealing a laminate to a support member (e.g., tray) where thelaminate has the recited free shrinks at both 200° F. and 240° F.reduces the amount and size of wrinkles (e.g., lid corrugations near thesealing area) and/or waves that may otherwise form in the lid of theresulting sealed package.

The laminate may provide enhanced seal strength relative to laminateshaving a barrier layer as an inner layer of the sealant film of thelaminate. It is believed that a barrier layer often presents a weakerinter-layer bond strength relative to the inter-layer bond strengths ofthe other layers. When a packaging seal fails, it is typically becauseof a delamination between layers having the weakest inter-layer bondstrength within a film of the laminate.

By placing the barrier layer in the outside film of the laminate, therelatively weaker inter-layer bond strength may be positioned fartherfrom the bond between the laminate and the support member. When suchpotential inter-layer failure is farther from the inside (i.e.,food-side) of the laminate, the failure tear propagation (i.e., the pathof inter-film cohesive failure) must travel farther to reach the“weakest link” inter-layer delamination path. This farther distance inthe present invention is believed to enhance the seal strength.

Further, the placement of barrier components in the outside film of thelaminate may allow for greater flexibility in manufacturing the lidstocklaminate. This is because the inside sealant film may be manufacturedwithout the additional restriction associated with accommodating barriercomponents in a coextruded, oriented film. For example, the extrusion ofa barrier layer often requires higher temperatures than those needed toextrude the other layers of the film. This higher temperature associatedwith a barrier layer may limit the amount of lower melting pointmaterials that can be used in the film—otherwise, the film may flow tooeasily and the melt strength may be lowered to an unacceptable level forprocessing. Also, the orientation of a film having a barrier layer mayrequire a higher orientation temperature, which can soften lower meltingpoint materials in the film to an unacceptable level, causing anunstable orientation or welding together of adjacent layers. Thus, theincorporation of the barrier components in the outside film allowsgreater choices in imparting the desired shrink and other attributes tothe inside, sealant film of the laminate.

The laminate may incorporate a trap print arrangement, which enhancesthe protection of the printed image of the laminate during the heat sealprocess that seals the laminate to a support member.

The laminate provides a low rate of oxygen transmission, which enablesthe atmosphere within the sealed package to be modified to extend theshelf life and bloom “color life” of a packaged red meat product. Thelaminate also provides excellent print quality and optical clarity.

The laminate can provide excellent sealability to a support member. Thisallows a packager to run the heat sealing machine at a fast rate whilealso providing good seal strength between the laminate and the tray. Theresulting seal between the laminate and the tray may provide excellentstrength even where the seal is formed in the presence of contaminantsand under variable heat sealing temperatures.

These and other objects, advantages, and features of the invention willbe more readily understood and appreciated by reference to the detaileddescription of the invention and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the sealed package of the presentinvention; and

FIG. 2 is a fragmentary, representational sectional view of theinventive laminate and sealed package of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The inventive laminate 10 comprises sealant film 12 laminated to barrierfilm 14 to trap print image 16 between the sealant and barrier films.Sealant film 12 may be monolayer, two-layer, or have three or morelayers (as shown in FIG. 1). Also, barrier film 14 may be monolayer,two-layer, or have three or more layers (as shown in FIG. 1). Thelaminate 10 may be sealed to support member 18 (e.g., a tray) to formsealed package 20 enclosing, for example, food product 22.

SEALANT FILM

The sealant film 12 defines an inside (i.e., food side) surface 24 andan outside surface 26 opposite the inside surface. The polymer material(i.e., component or blend of components) that forms the inside surface24 of the sealant film has a melting point that facilitates heat sealingthe laminate 10 to a support member 18. If the sealant film ismonolayer, then it may have the composition, attributes, and physicalcharacteristics as discussed in conjunction with the Sealant Layersection below.

The sealant film 12 may have any total thickness as long as it providesthe desired properties (e.g., flexibility, Young's modulus, optics,strength) for the given packaging application of expected use. Thesealant film may have a thickness of less than about any of thefollowing: 10 mils, 5 mils, 4 mils, 3 mils, 2 mils, 1.5 mils, 1.4 mils,1.3 mils, 1.2 mils, 1.1 mils, and 1 mil. (A “mil” is equal to 0.001inch.) The sealant film may also have a thickness of at least about anyof the following: 0.3 mils, 0.4 mils, 0.5 mils, 0.6 mils, 0.7 mils, 0.75mils, 0.8 mils, 0.9 mils, 1 mil, 1.2 mil, 1.4 mil, and 1.5 mil. Thesealant film may have a thickness of at least about any of the followingpercentages of the thickness of the barrier film: 50%, 60%, 70%, 80%,90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, and 175%. For example,the thickness of the sealant film may be greater than or equal to thethickness of the barrier film.

The sealant film 12 may be relatively permeable to oxygen relative tothe barrier film 14 discussed below. For example, the sealant film 12may have an oxygen transmission rate higher than that of the barrierfilm 14 by at least about any of the following: 50, 75, 100, 200, 500,and 1,000 cubic centimeters (at standard temperature and pressure) persquare meter per day per 1 atmosphere of oxygen pressure differentialmeasured at 0% relative humidity and 23° C., measured according to ASTMD-3985. Also, the sealant film 12 may have an oxygen transmission rateof at least about any of the following: 110, 200, 500, 1,000, 2,000,3,000, 5,000, 10,000, 15,000, 20,000, and 50,000 cubic centimeters (atstandard temperature and pressure) per square meter per day per 1atmosphere of oxygen pressure differential measured at 0% relativehumidity and 23° C., measured according to ASTM D-3985.

The sealant film 12 has a heat-shrinkable attribute. For example, thesealant film 12 may have a free shrink measured at 200° F. in at leastone direction (i.e., machine or transverse direction), in at least eachof two directions (machine and transverse directions), or a total freeshrink of at least about any of the following values: 5%, 7%, 10%, 15%,20%, 30%, 40%, 50%, and 60%. Also, sealant film 12 may have a freeshrink measured at 240° F. in at least one direction (machine ortransverse directions), in each of at least two directions (machine andtransverse directions), or a total free shrink measured of at leastabout any of the following values: 7%, 10%, 15%, 20%, 25%, 30%, 40%,50%, 55%, 60%, 65%, and 70%.

As is known in the art, the total free shrink is determined by summingthe percent free shrink in the machine (longitudinal) direction with thepercentage of free shrink in the transverse direction. For example, afilm which exhibits 50% free shrink in the transverse direction and 40%free shrink in the machine direction has a total free shrink of 90%.

Unless otherwise indicated, each reference to free shrink in thisapplication means a free shrink determined by measuring the percentdimensional change in a 10 cm×10 cm specimen when subjected to selectedheat (i.e., at a certain temperature exposure) according to ASTM D 2732.Also, a reference herein to the shrink attributes of a film that is acomponent of a laminate refers to the shrink attributes of the filmitself, which can be measured by separating the film from thelaminate—for example, by using an appropriate solvent to dissolve theadhesive that bonds the films together to form the laminate.

The sealant or first film 12 is preferably multilayer (i.e., includestwo or more layers) so that the layers in combination impart the desiredperformance characteristics to the sealant film. The sealant film 12may, for example, comprise from 2 to 15 layers, at least 3 layers, atleast 4 layers, at least 5 layers, from 2 to 4 layers, from 2 to 5layers, and from 5 to 9 layers. As used herein, the term “layer” refersto a discrete film component which is coextensive with the film and hasa substantially uniform composition.

A multilayer sealant film includes a sealant layer 28 forming thefood-side or inside surface and a skin or print-side layer 30 formingthe outside or non-food surface of the sealant film. The multilayersealant film may also include one or more additional layers 32, such ascore, bulk, and tie layers, although the sealant film may have acomposition such that tie layers are not incorporated in the sealantfilm.

Below are some examples of combinations in which the alphabeticalsymbols designate the resin layers. Where the multilayer sealant filmrepresentation below includes the same letter more than once, eachoccurrence of the letter may represent the same composition or adifferent composition within the class that performs a similar function.

A/D, A/C/D, A/B/D, A/B/C/D, A/C/B/D, A/B/B/D, A/C/B/C/D, A/B/B/B/D,A/B/C/B/D, A/C/B/B/D, A/C/B/B/C/D, A/B/C/B/C/D, A/C/B/C/B/D,A/B/C/B/B/D, A/C/B/B/B/D, A/C/B/C/B/D, A/C/B/B/B/C/D

“A” is the sealant layer (heat seal layer), as discussed below.

“B” is a core or bulk layer, as discussed below.

“C” is a tie layer, as discussed below.

“D” is an skin or print-side layer, as discussed below.

Sealant Layer of the Sealant Film

Sealant layer 28 forms the inside surface 24 of the laminate 10. Sealantlayer 28 facilitates the heat-sealing of laminate 10 to another object,such as a support member or tray 18. The sealant layer preferablyincludes selected components having a melt or softening point lower thanthat of the components of the other layers of the sealant film. Thesealant layer may comprise a resin having a Vicat softening temperatureof less than about any of the following values: 120° C., 115° C., 110°C., 105° C., 100° C., 95° C., and 90° C. The sealant layer may includeone or more polymers having a melt-flow index of at least about any ofthe following: 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.5, 4, 5, 6,7, 8, 9, 10, 15, and 20. The sealant layer may include one or morepolymers having a melting point of less than about any of the following:130° C., 125° C., 120° C., 115° C., 112° C., 110° C., 108° C., 105° C.,103° C., 100° C., 98° C., and 95° C., in an amount of at least about anyof the following percentages (based on the weight of the sealant layer):30, 40, 50, 60, 70, 80, 90, and 100.

All references to “Vicat” values in this application are measuredaccording to ASTM 1525 (1 kg). All references to melt-flow index in thisapplication are measured according to ASTM D1238, at a temperature andpiston weight as specified according to the material as set forth in theASTM test method. All references to the melting point of a polymer orresin in this application refers to the melting peak temperature of thedominant melting phase of the polymer or resin as determined bydifferential scanning calorimetry according to ASTM D-3418.

The sealant layer may include one or more thermoplastic polymersincluding polyolefins, polystyrenes, polyurethanes, polyamides,polyesters, polyvinyl chlorides, and ionomers.

Useful polyolefins include ethylene homo- and co-polymers and propylenehomo- and co-polymers. Ethylene homopolymers include high densitypolyethylene (“HDPE”) and low density polyethylene (“LDPE”). Ethylenecopolymers include ethylene/alpha-olefin copolymers (“EAOs”),ethylene/unsaturated ester copolymers, and ethylene/(meth)acrylic acid.(“Copolymer” as used in this application means a polymer derived fromtwo or more types of monomers, and includes terpolymers, etc.)

EAOs are copolymers of ethylene and one or more alpha-olefins, thecopolymer having ethylene as the majority mole-percentage content.Preferably, the comonomer includes one or more C₃-C₂₀ α-olefins, morepreferably one or more C₄-C₁₂ α-olefins, and most preferably one or moreC₄-C₈ α-olefins. Particularly preferred α-olefins include 1-butene,1-hexene, 1-octene, and mixtures thereof.

EAOs include one or more of the following: 1) medium densitypolyethylene (“MDPE”), for example having a density of from 0.93 to 0.94g/cm3; 2) linear medium density polyethylene (“LMDPE”), for examplehaving a density of from 0.926 to 0.94 g/cm3; 3) linear low densitypolyethylene (“LLDPE”), for example having a density of from 0.915 to0.930 g/cm3; 4) very-low or ultra-low density polyethylene (“VLDPE” and“ULDPE”), for example having density below 0.915 g/cm3, and 5)homogeneous EAOs. Useful EAOs include those having a density of lessthan about any of the following: 0.925, 0.922, 0.92, 0.917, 0.915,0.912, 0.91, 0.907, 0.905, 0.903, 0.9, and 0.898 grams/cubic centimeter.Unless otherwise indicated, all densities herein are measured accordingto ASTM D1505.

The polyethylene polymers may be either heterogeneous or homogeneous. Asis known in the art, heterogeneous polymers have a relatively widevariation in molecular weight and composition distribution.Heterogeneous polymers may be prepared with, for example, conventionalZiegler Natta catalysts.

On the other hand, homogeneous polymers are typically prepared usingmetallocene or other single site-type catalysts. Such single-sitecatalysts typically have only one type of catalytic site, which isbelieved to be the basis for the homogeneity of the polymers resultingfrom the polymerization. Homogeneous polymers are structurally differentfrom heterogeneous polymers in that homogeneous polymers exhibit arelatively even sequencing of comonomers within a chain, a mirroring ofsequence distribution in all chains, and a similarity of length of allchains. As a result, homogeneous polymers have relatively narrowmolecular weight and composition distributions. Examples of homogeneouspolymers include the metallocene-catalyzed linear homogeneousethylene/alpha-olefin copolymer resins available from the Exxon ChemicalCompany (Baytown, Tex.) under the EXACT trademark, linear homogeneousethylene/alpha-olefin copolymer resins available from the MitsuiPetrochemical Corporation under the TAFMER trademark, and long-chainbranched, metallocene-catalyzed homogeneous ethylene/alpha-olefincopolymer resins available from the Dow Chemical Company under theAFFINITY trademark.

Another useful ethylene copolymer is ethylene/unsaturated estercopolymer, which is the copolymer of ethylene and one or moreunsaturated ester monomers. Useful unsaturated esters include: 1) vinylesters of aliphatic carboxylic acids, where the esters have from 4 to 12carbon atoms, and 2) alkyl esters of acrylic or methacrylic acid(collectively, “alkyl (meth)acrylate”), where the esters have from 4 to12 carbon atoms.

Representative examples of the first (“vinyl ester”) group of monomersinclude vinyl acetate, vinyl propionate, vinyl hexanoate, and vinyl2-ethylhexanoate. The vinyl ester monomer may have from 4 to 8 carbonatoms, from 4 to 6 carbon atoms, from 4 to 5 carbon atoms, andpreferably 4 carbon atoms.

Representative examples of the second (“alkyl (meth)acrylate”) group ofmonomers include methyl acrylate, ethyl acrylate, isobutyl acrylate,n-butyl acrylate, hexyl acrylate, and 2-ethylhexyl acrylate, methylmethacrylate, ethyl methacrylate, isobutyl methacrylate, n-butylmethacrylate, hexyl methacrylate, and 2-ethylhexyl methacrylate. Thealkyl (meth)acrylate monomer may have from 4 to 8 carbon atoms, from 4to 6 carbon atoms, and preferably from 4 to 5 carbon atoms.

The unsaturated ester (i.e., vinyl ester or alkyl (meth)acrylate)comonomer content of the ethylene/unsaturated ester copolymer may rangefrom about 6 to about 18 weight %, and from about 8 to about 12 weight%, based on the weight of the copolymer. Useful ethylene contents of theethylene/unsaturated ester copolymer include the following amounts: atleast about 82 weight %, at least about 85 weight %, at least about 88weight %, no greater than about 94 weight %, no greater than about 93weight %, and no greater than about 92 weight %, based on the weight ofthe copolymer.

Representative examples of ethylene/unsaturated ester copolymers includeethylene/methyl acrylate, ethylene/methyl methacrylate, ethylene/ethylacrylate, ethylene/ethyl methacrylate, ethylene/butyl acrylate,ethylene/2-ethylhexyl methacrylate, and ethylene/vinyl acetate.

Another useful ethylene copolymer is ethylene/(meth)acrylic acid, whichis the copolymer of ethylene and acrylic acid, methacrylic acid, orboth.

Useful propylene copolymer includes propylene/ethylene copolymers(“EPC”), which are copolymers of propylene and ethylene having amajority weight % content of propylene, such as those having an ethylenecomonomer content of less than 10%, preferably less than 6%, and morepreferably from about 2% to 6% by weight.

Useful polyesters and polyamides include those described in thisapplication below.

Ionomer is a copolymer of ethylene and an ethylenically unsaturatedmonocarboxylic acid having the carboxylic acid groups partiallyneutralized by a metal ion, such as sodium or zinc, preferably zinc.Useful ionomers include those in which sufficient metal ion is presentto neutralize from about 15% to about 60% of the acid groups in theionomer. The carboxylic acid is preferably “(meth)acrylic acid”—whichmeans acrylic acid and/or methacrylic acid. Useful ionomers includethose having at least 50 weight % and preferably at least 80 weight %ethylene units. Useful ionomers also include those having from 1 to 20weight percent acid units. Useful ionomers are available, for example,from Dupont Corporation (Wilmington, Del.) under the SURLYN trademark.

The sealant layer 28 may have a composition such that any one of theabove described polymers comprises at least about any of the followingweight percent values: 30, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90,95, and 100% by weight of the layer.

The thickness of the sealant layer is selected to provide sufficientmaterial to effect a strong heat seal bond, yet not so thick so as tonegatively affect the manufacture (i.e., extrusion) of the sealant filmby lowering the melt strength of the film to an unacceptable level. Thesealant layer may have a thickness of at least about any of thefollowing values: 0.2 mils, 0.25 mils, 0.3 mils, 0.35 mils, 0.4 mils,0.45 mils, 0.5 mils, and 0.6 mils. The sealant layer may have athickness ranging from about 0.05 to about 6 mils, more preferably fromabout 0.1 to about 2 mils, and still more preferably from about 0.2 toabout 0.5 mils. Further, the thickness of the sealant layer as apercentage of the total thickness of the sealant film may range (inascending order of preference) from about 1 to about 50 percent, fromabout 5 to about 45 percent, from about 10 to about 45 percent, fromabout 15 to about 40 percent, from about 15 to about 35 percent, andfrom about 15 to about 30 percent. The sealant layer may have athickness relative to the thickness of the sealant film of at leastabout any of the following values: 15%, 20%, 30%, 40%, and 50%.

Skin Layer of the Sealant Film

The skin layer 30 of the sealant film may provide the surface upon whicha printed image (e.g., printed information) is applied, in which casethe layer is preferably capable of providing a surface that iscompatible with the selected print ink system. Further, the skin layer30 provides the outside surface 26 to which the barrier film 14 may bedirectly laminated, as discussed in more detail below.

The skin layer 30 may include any of the thermoplastics or compositionsas discussed above in conjunction with the sealant layer 28. The skinlayer 30 may have a composition or thickness (or both) substantiallysimilar to the sealant layer 28; or, the skin layer 30 may have athickness and/or composition different from the sealant layer 28. Forexample, the skin layer 30 may comprise one or more polymers having amelting point higher than the melting point of the lowest melting pointpolymer of the sealant layer 28 by at least about any of the followingvalues: 3° F., 5° F., 7° F., 10° F., 15° F., 20° F., 25° F., 30° F., and35° F. The one or more higher melting point polymers of the skin layermay comprise a weight percentage of the skin layer of at least about anyof the following values: 30, 40, 50, 60, 70, 75, 80, 85, 90, 95%.

Further, the one or more polymers of the skin layer 30 having a lowestmelting point of the polymers of the skin layer may also have a meltingpoint higher than the one or more polymers of the sealant layer 38having a lowest melting point of the polymers of the sealant layer. Forexample, the lowest melting point polymer of the skin layer may have amelting point higher by at least about any of the following values: 3°F., 5° F., 7° F., 10° F., 15° F., 20° F., 25° F., 30° F., and 35° F.This differential in melting point values generally results in the skinlayer 30 having lower tackiness than the sealant layer 28, since ahigher melting point polymer generally has less tackiness than a lowermelting point polymer. As a result, the manufacture of the sealant filmmay be facilitated, because the sealant film is less likely to stick toitself when wound into a roll—and less likely to cause a reduction inprocessing speeds by sticking to processing equipment.

The skin layer 30 may include one or more of any of the above-describedpolymers, for example, polyamides, polyethylene, and/or polypropylene,either alone or in combination. The skin layer 30 may have a compositionsuch that any one of the above-described polymers comprises at leastabout any of the following weight percent values: 30, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, and 100% by weight of the layer.

The skin layer may have a thickness of from about 0.05 to about 5 mils,preferably from about 0.2 to about 2 mils, and more preferably fromabout 0.2 to about 0.5 mils. The thickness of the skin layer may rangeas a percentage of the total thickness of the sealant film of from about(in ascending order of preference) 1 to 50 percent, 3 to 45 percent, 5to 40 percent, 7 to 35 percent, and 7 to 30 percent. Useful thicknessesfor the skin layer include at least about any of the following values:0.1 mils, 0.15 mils, 0.2 mils, and 0.25 mils.

Additional Layers of the Sealant Film

The sealant film 12 may include one or more additional layers 32, suchas a tie, core, or bulk layers. A tie layer is an inner film layerhaving the primary purpose of adhering two layers of a film together.The tie layers, if present in the sealant film, may have the compositionand other attributes as described below in conjunction with the tielayers of barrier film 14. The adjacent layers of a multiple layersealant film 12 may have sufficient compatibility so that a tie layer isnot needed to form a inter-layer bond strength that is sufficientlystrong for the expected end use.

A core or bulk layer may be an inner film layer having a primary purposeother than as a barrier or tie layer—for example, serving to provide amultilayer film with a desired level of strength, modulus, or optics. Acore or bulk layer may include one or more of the polymers and/or have acomposition as described above in the Sealant Layer section with respectto the sealant layer.

Each of the additional layers 32 may have a thickness of from about 0.05to about 5 mils, preferably from about 0.1 to about 2 mils, and morepreferably from about 0.2 to about 0.5 mils. The thickness of anadditional layer may range as a percentage of the total thickness of thesealant film of from about (in ascending order of preference) 1 to 80percent, 3 to 50 percent, 5 to 40 percent, 7 to 35 percent, and 7 to 30percent. Preferably, adjacent film layers have different compositions.

Carrier Film

The barrier film 14 defines an inside surface 34 and an outside surface36 opposite the inside surface. The outside surface 36 of the barrierfilm 14 forms the surface that may engage the heated bar of aheat-sealing device (not shown) used in sealing laminate 10 to supportmember 18, as discussed in more detail below. The outside layer 40 formsthe outside surface 36 of the barrier film.

The barrier film 14 may have any total thickness as long as it providesthe desired properties (e.g., flexibility, Young's modulus, optics,strength, barrier) for the given packaging application of expected use.The barrier film may have a thickness of less than about any of thefollowing: 10 mils, 5 mils, 4 mils, 3 mils, 2 mils, 1.5 mils, 1.2 mils,and 1.1 mils. The barrier film may also have a thickness of at leastabout any of the following: 0.25 mils, 0.3 mils, 0.35 mils, 0.4 mils,0.45 mils, 0.5 mils, 0.6 mils, 0.75 mils, 0.8 mils, 0.9 mils, 1 mil, 1.2mils, 1.4 mils, and 1.5 mils.

The barrier film 14 preferably has a composition that imparts oxygenbarrier attributes to the barrier film. Examples of the components thatare useful in imparting decreased oxygen barrier properties to the film(i.e., “barrier components”) are discussed below in the Barrier Layersection. If the barrier film 14 is multilayer, then the one or morelayers of the film that incorporate barrier components sufficient todecrease the oxygen permeability of the film are considered “barrierlayers.” If the barrier film is monolayer, then the barrier componentsmay be incorporated in the sole layer of the barrier film, in which casethe monolayer barrier film itself would be considered the “barrierlayer.” In such case, the barrier layer may also provide one or moreadditional functions, such as the inside, outside (abuse), bulk, and/orcore layers of the barrier film. Accordingly, if the barrier film 14 ismonolayer, then it may have the composition, attributes, and physicalcharacteristics as discussed in conjunction with any of the BarrierLayer, Abuse Layer, or Inside Layer sections below.

Useful oxygen transmission rates for the barrier film 14 and laminate 10are discussed below in the Barrier Layer section.

The barrier film 14 has a heat-shrinkable attribute. For example, thebarrier film 14 may have a free shrink measured at 200° F. in at leastone direction (i.e., machine or transverse direction), in at least eachof two directions (machine and transverse directions), or a total freeshrink of at least about any of the following values: 5%, 7%, 10%, 15%,20%, 30%, 40%, 50%, and 60%. Also, barrier film 14 may have a freeshrink measured at 240° F. in at least one direction (machine ortransverse directions), in each of at least two directions (machine andtransverse directions), or a total free shrink measured of at leastabout any of the following values: 7%, 10%, 15%,20%, 25%, 30%, 40%, 50%,55%, 60%, 65%, and 70%.

The ratio of free shrink of the barrier film 14 to the free shrink ofthe sealant film 12, measured at the same temperature and in the samedirection, may be calculated for shrink temperatures of 200° F. and 240°F. in each of the machine and transverse directions. Each of theresulting ratios may be at least about any of the following values: 0.3,0.4, 0.5, 0.6, and 0.75—and at most about any of the following values:3, 2.5, 2, 1.8, and 1.5. It is believed that heat sealing a laminate toa support member (e.g., tray) where the laminate comprises first andsecond films with free shrinks within these ranges of ratios reduces theamount and size of wrinkles and/or waves that may otherwise form in thelid of the resulting sealed package.

The barrier film 14 comprises one or more polymers forming the outsidesurface 36, where the one or more polymers may have a melting pointgreater than that of the lowest melting point polymer of the sealantlayer 28—for example, greater by at least about any of the followingvalues: 25° F., 30° F., 40° F., 50° F., 65° F., 70° F., 80° F., 90° F.,and 100° F. Further, outside layer 40 may comprise one or more polymershaving a melting point greater than that of the lowest melting pointpolymer of the sealant layer 28—for example, greater by at least aboutany of the following values: 25° F., 30° F., 40° F., 50° F., 65° F., 70°F., 80° F., 90° F., and 100° F. The lowest melting point polymer of theoutside layer 40 may have a melting point higher than the lowest meltingpoint polymer of the sealant layer 28, for example, higher by at leastabout any of the following values: 25° F., 30° F., 40° F., 50° F., 65°F., 70° F., 80° F., 90° F., and 100° F. The amount of the one or morepolymers of the outside layer 40 having either: 1) a melting pointgreater than that of the lowest melting point polymer of the sealantlayer 28 or 2) having the lowest melting point of the outside layer 40may comprise a weight percentage of the outside layer 40 of at leastabout any of the following values: 40, 50, 60, 70, 75, 80, 85, 90, 95%,100%.

The barrier or second film 14 is preferably multilayer so that thelayers in combination impart the desired performance characteristics tothe barrier film. The barrier film 14 may comprise multiple layers, forexample 2 layers, from 2 to 15 layers, 3 layers, at least 3 layers, atleast 4 layers, at least 5 layers, from 2 to 4 layers, from 2 to 5layers, and from 5 to 9 layers.

A multilayer barrier film includes: i) an inside layer 38 forming theinside surface 34 of the barrier film—a layer that upon lamination isproximate the outside layer 26 of the sealant film 12 and ii) an abuseor outside layer 40 forming the outside surface 36 of the barrier film14. The inside layer 38 may be directly adhered to the outside layer 40.Alternatively, one or more inner layers 42, such as barrier, tie, core,and bulk layers, may exist between the inside layer 38 and the outsidelayer 40. Further, a barrier layer may be directly adhered to outsidelayer 40. The barrier layer may be a coated barrier layer, that is, abarrier layer formed by coating onto to another layer, for example,directly coated onto the inside surface of abuse layer 40 or as anexterior layer of the barrier film.

Below are some examples of layer combinations for the multiple layerbarrier film 14 in which the alphabetical symbols designate the resinlayers. Where the multilayer barrier film representation below includesthe same letter more than once, each occurrence of the letter mayrepresent the same composition or a different composition within theclass that performs a similar function.

E/G, G/F, E/G/F, E/C/G, G/C/F, E/B/G, G/B/F, E/G/C/F, E/C/G/F,E/C/G/C/F, E/C/B/G/B/F, E/C/B/G, G/C/B/F, E/C/B/G/B/C/F

“B” is a core or bulk layer, as discussed above with respect to thesealant film.

“C” is a tie layer, as discussed below.

“E” is the inside layer of the barrier film, as discussed below. (If “E”is not present, then the first letter represents the inside layer, forexample if “G” is the first letter, then the inside layer is also abarrier layer. Layer “E” may comprise any of the thermoplastics orcompositions discussed above in the Sealant Layer section.)

“F” is an outside or abuse layer of the barrier film, as discussedbelow. (If “F” is not present, then the last letter represents theoutside layer, for example if “G” is the last letter, then the outside,abuse layer is also a barrier layer. Layer “F” may comprise any of thethermoplastics or compositions discussed above in the Sealant Layersection.)

“G” is a barrier layer, as discussed below.

Barrier Layer of the Barrier Film

The barrier film 14 may include one or more barrier layers, whichincorporate one or more components (“barrier components”) that markedlydecrease the oxygen transmission rate through the layer and thus thefilm incorporating such layer. Accordingly, the barrier layer of thefilm that is utilized in a lidstock laminate incorporated in a packagemay either help to exclude oxygen from the interior of the package—or tomaintain oxygen within the package.

Useful barrier components include: ethylene/vinyl alcohol copolymer(“EVOH”), polyvinyl alcohol (“PVOH”), vinylidene chloride polymers(“PVdC”), polyalkylene carbonate, polyester (e.g., PET, PEN),polyacrylonitrile (“PAN”), and polyamide.

EVOH may have an ethylene content of between about 20% and 40%,preferably between about 25% and 35%, more preferably about 32% byweight. EVOH may include saponified or hydrolyzed ethylene/vinyl acetatecopolymers, such as those having a degree of hydrolysis of at least 50%,preferably of at least 85%.

Vinylidene chloride polymer (“PVdC”) refers to a vinylidenechloride-containing polymer or copolymer—that is, a polymer thatincludes monomer units derived from vinylidene chloride (CH₂═CCl₂) andalso, optionally, monomer units derived from one or more of vinylchloride, styrene, vinyl acetate, acrylonitrile, and C₁-C₁₂ alkyl estersof (meth)acrylic acid (e.g., methyl acrylate, butyl acrylate, methylmethacrylate). As used herein, “(meth)acrylic acid” refers to bothacrylic acid and/or methacrylic acid; and “(meth)acrylate” refers toboth acrylate and methacrylate. Examples of PVdC include one or more ofthe following: vinylidene chloride homopolymer, vinylidenechloride/vinyl chloride copolymer (“VDC/VC”), vinylidene chloride/methylacrylate copolymer, vinylidene chloride/ethyl acrylate copolymer,vinylidene chloride/ethyl methaerylate copolymer, vinylidenechloride/methyl methacrylate copolymer, vinylidene chloride/butylacrylate copolymer, vinylidene chloride/styrene copolymer, vinylidenechloride/acrylonitrile copolymer, and vinylidene chloride/vinyl acetatecopolymer.

Useful PVdC includes that having between 75 and 95 weight % vinylidenechloride monomer. Useful PVdC includes that having from about 5 to about25 weight %, from about 10 to about 22 weight %, and from about 15 toabout 20 weight % comonomer with the vinylidene chloride monomer. UsefulPVdC includes that having a weight-average molecular weight (M_(w)) ofat least 80,000, such as at least 90,000, at least 100,000, at least111,000, at least 120,000, at least 150,000, and at least 180,000; andbetween 80,000 and 180,000, such as between 90,000 and 170,000, between100,000 and 160,000, between 111,000 and 150,000, and between 120,000and 140,000. Useful PVdC also includes that having a viscosity-averagemolecular weight (M_(z)) of at least 130,000, such as at least 150,000,at least 170,000, at least 200,000, at least 250,000, and at least300,000; and between 130,000 and 300,000, such as between 150,000 and270,000, between 170,000 and 250,000, and between 190,000 and 240,000.

A barrier layer that includes PVdC may also include a thermal stabilizer(e.g., a hydrogen chloride scavenger such as epoxidized soybean oil) anda lubricating processing aid (e.g., one or more acrylates).

Useful polyamides include polyamide 6, polyamide 9, polyamide 10,polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 612,polyamide 6I, polyamide 6T, polyamide 69, copolymers made from any ofthe monomers used to make two or more of the foregoing homopolymers(e.g., copolyamide 6/12, polyamide 12, copolyamide 66/69/6I, copolyamide66/610, copolyamide 6/66, and copolyamide 6/69), and blends of any ofthe foregoing homo- and/or copolymers. Polyamide copolymers include: (a)copolyamide 6/12 comprising (i) caprolactam mer in an amount of fromabout 20 to 80 weight percent (preferably 30 to 70 weight percent, morepreferably 40 to 60 weight percent), and (ii) laurolactam mer in anamount of from about 80 to 20 weight percent; and (b) copolyamide66/69/6I comprising 10 to 50 weight percent hexamethylene adipamide mer(preferably from about 20 to 40 weight percent), 10 to 50 weight percentpolyamide 69 mer (preferably from about 20 to 40 weight percent), and 10to 60 weight percent hexamethylene isophthalamide mer (preferably, fromabout 10 to 40 weight percent).

Useful polyesters include those described in the Abuse Layer sectionbelow.

A barrier layer preferably has a thickness and composition sufficient toimpart either to barrier film 14 or to laminate 10 incorporating thebarrier film an oxygen transmission rate of no more than about any ofthe following values: 100, 50, 45, 40, 35, 30, 25, 20, 15, 10, and 5cubic centimeters (at standard temperature and pressure) per squaremeter per day per 1 atmosphere of oxygen pressure differential measuredat 0% relative humidity and 23° C. All references to oxygen transmissionrate in this application are measured at these conditions according toASTM D-3985. (A reference to the oxygen transmission attributes of afilm that is a component of a laminate refers to the oxygen transmissionattributes of the film itself, which can be measured by separating thefilm from the laminate—for example, by using an appropriate solvent todissolve the adhesive that bonds the films together to form thelaminate.)

A barrier layer may also be formed from a latex emulsion coating gradeof vinylidene chloride/vinyl chloride copolymer having 5-15% vinylchloride. The coating grade copolymer of vinylidene chloride/vinylchloride may be present in an amount of from 5-100% (of total solids)with the remainder being 2-10% epoxy resin and melt extrusion gradematerial.

The barrier layer may comprise barrier component in an amount of atleast about any of the following: 50%, 60%, 70%, 80%, 90%, and 100%,based on the weight of the barrier layer. The barrier layer thicknessmay range from about any of the following: about 0.05 to about 6 mils,about 0.05 to about 4 mils, about 0.1 to about 3 mils, and about 0.12 to2 mils.

Abuse Layer of the Barrier Film

The barrier film 14 may be exposed to environmental stresses, forexample once the barrier film is incorporated into laminate 10 andformed into a package 20. Such environmental stresses include abrasionand other abuse during processing and shipment. The outside or abuselayer 40 preferably provides enhanced resistance to abuse. Since theabuse layer 40 may be directly exposed to the heat seal bar of theheat-sealing equipment (not shown) when forming the sealed package 20,the abuse layer preferably provides heat-resistant characteristics tothe barrier film 14 (and laminate 10) to help prevent “burn-through”during heat sealing. This is because in forming package 20 byconductance heat sealing the laminate 10 to support member 18, sealantlayer 28 is placed in contact with the support member 18, while theoutside layer 40 is proximate the heated bar of the heat sealingapparatus. The heat seal bar transfers heat through the outside layer40, through laminate 10, to the sealant layer 28 to form the heat seal44 between the laminate and support member. Accordingly, outside layer40 may be exposed to the highest temperature during the sealingoperation. Useful melting point attributes for the abuse or outsidelayer 40 have been discussed above.

The abuse layer 40 may include one or more of any of the following:polyolefins (e.g., polyethylenes, polypropylenes), polyamides,polyesters, polystyrenes, polyurethanes, and polycarbonates. Forexample, the abuse layer may include any of these polymers in an amountof at least 50 weight %, more preferably at least 70%, still morepreferably at least 90%, and most preferably 100% by weight of thelayer.

Examples of suitable polyesters include amorphous (co)polyesters,poly(ethylene/terephthalic acid), and poly(ethylene/naphthalate).Poly(ethylene/terephthalic acid) with at least about 75 mole percent,more preferably at least about 80 mole percent, of its mer units derivedfrom terephthalic acid may be preferred.

Useful polyamides, polyethylenes, and polypropylenes include thosedescribed above.

The outside layer 40 may have a thickness of from about 0.05 to about 5mils, preferably from about 0.3 to about 4 mils, and more preferablyfrom about 0.5 to about 3.5 mils. The thickness of the outside layer mayrange as a percentage of the total thickness of the barrier film fromabout (in ascending order of preference) 1 to 50 percent, 3 to 45percent, 5 to 40 percent, 7 to 35 percent, and 7 to 30 percent. Usefulthicknesses for the outside layer include at least about any of thefollowing values: 0.05 mils, 0.1 mils, 0.15 mils, 0.2 mils, 0.25 mils,0.3 mils, 0.35 mils, and 0.4 mils.

Tie Layer of the Barrier Film

The barrier film 14 may include one or more tie layers, which have theprimary purpose of improving the adherence of two layers of a film toeach other. Tie layers may include polymers having grafted polar groupsso that the polymer is capable of covalently bonding to polar polymers.Useful polymers for tie layers include ethylene/unsaturated acidcopolymer, ethylene/unsaturated ester copolymer, anhydride-modifiedpolyolefin, polyurethane, and mixtures thereof. Preferred polymers fortie layers include one or more of ethylene/vinyl acetate copolymerhaving a vinyl acetate content of at least 15 weight %, ethylene/methylacrylate copolymer having a methyl acrylate content of at least 20weight %, anhydride-modified ethylene/methyl acrylate copolymer having amethyl acrylate content of at least 20%, and anhydride-modifiedethylene/alpha-olefin copolymer, such as an anhydride grafted LLDPE.

Modified polymers or anhydride-modified polymers include polymersprepared by copolymerizing an unsaturated carboxylic acid (e.g., maleicacid, fumaric acid), or a derivative such as the anhydride, ester, ormetal salt of the unsaturated carboxylic acid with—or otherwiseincorporating the same into—an olefin homopolymer or copolymer. Thus,anhydride-modified polymers have an anhydride functionality achieved bygrafting or copolymerization.

The barrier film 14 may also include a tie layer directly adhered (i.e.,directly adjacent) to one or both sides of an internal barrier layer.Further, a tie layer may be directly adhered to the inner (food-side)surface of the outside layer 40. The tie layers are of a sufficientthickness to provide the adherence function, as is known in the art.Each tie layer may be of a substantially similar or a differentcomposition and/or thickness.

Inside Layer of the Barrier Film

The inside layer 38 of the barrier film 14 may provide the surface uponwhich a printed image (e.g., printed information) is applied, in whichcase the inside layer is preferably capable of providing a surface thatis compatible with the selected print ink system. Further, the insidelayer 38 provides the inside surface 34 to which the sealant film 12 maybe directly laminated, as discussed in more detail below. The insidelayer 38 may be a barrier layer.

The inside layer 38 may include any of the thermoplastics orcompositions as discussed above in conjunction with the sealant layer 28of the sealant film 12. The inside layer 38 may have a thickness of fromabout 0.05 to about 5 mils, preferably from about 0.1 to about 2 mils,and more preferably from about 0.2 to about 0.5 mils. The thickness ofthe inside layer 38 may range as a percentage of the total thickness ofthe barrier film 14 of from about (in ascending order of preference) 1to 50 percent, 3 to 45 percent, 5 to 40 percent, 7 to 35 percent, and 7to 30 percent. Useful thicknesses for the inside layer include at leastabout any of the following values: 0.1 mils, 0.15 mils, 0.2 mils, and0.25 mils.

Bond Strengths of the Sealant and/or Barrier Films

The term “inter-layer bond strength” as used herein means the amount offorce required to separate or delaminate two adjacent film layers byadhesive failure, as measured in accordance with ASTM F88-94 where theInstron tensile tester crosshead speed is 5 inches per second, usingfive, 1-inch wide, representative samples. The weakest of theinter-layer bond strength of either or both of the sealant film andbarrier film may be at least about any of the following: 0.2, 0.3, 0.4,0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 pounds/inch.

The term “intra-layer cohesive strength” as used herein means the amountof force required to separate a film layer by cohesive failure, asmeasured in a direction that is perpendicular to the plane of the filmand in accordance with ASTM F88-94 where the Instron tensile testercrosshead speed is 5 inches per second, using five, 1-inch wide,representative samples.

The term “intra-film cohesive strength” refers to the internal forcewith which a film remains intact, as measured in a direction that isperpendicular to the plane of the film. In a multilayer film, intra-filmcohesive strength is provided both by inter-layer adhesion (the adhesivestrength between the layers which binds them to one another) and by theintra-layer cohesion of each film layer (i.e., the cohesive strength ofeach of the film layers). In a monolayer film, intra-film cohesivestrength is provided only by the intra-layer cohesion of the layer whichconstitutes the film. The weakest of the intra-film cohesive strength ofeither or both of the sealant film and barrier film may be at leastabout any of the following: 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 pounds/inch.

Additives of Sealant and/or Barrier Films

One or more layers of the sealant and or barrier films of laminate 10may include one or more additives useful in packaging films, such as,antiblocking agents, slip agents, antifog agents, colorants, pigments,dyes, flavorants, antimicrobial agents, meat preservatives,antioxidants, fillers, radiation stabilizers, and antistatic agents.Such additives, and their effective amounts, are known in the art.

An antifog agent may advantageously be incorporated into sealant layer28 or coated onto sealant layer 28, because sealant layer 28 forms theinside layer adjacent the interior of the sealed package 20. Theincorporation of the antifog agent may occur either before or afterlamination of the barrier film to the sealant film. Suitable antifogagents may fall into classes such as esters of aliphatic alcohols,esters of polyglycol, polyethers, polyhydric alcohols, esters ofpolyhydric aliphatic alcohols, polyethoxylated aromatic alcohols,nonionic ethoxylates, and hydrophilic fatty acid esters. Useful antifogagents include polyoxyethylene, sorbitan monostearate, polyoxyethylenesorbitan monolaurate, polyoxyethylene monopalmitate, polyoxyethylenesorbitan tristearate, polyoxyethylene sorbitan trioleate,poly(oxypropylene), polyethoxylated fatty alcohols, polyoxyethylated4-nonylphenol, polyhydric alcohol, propylene diol, propylene triol, andethylene diol, monoglyceride esters of vegetable oil or animal fat,mono- and/or diglycerides such as glycerol mono- and dioleate, glycerylstearate, monophenyl polyethoxylate, and sorbitan monolaurate. Theantifog agent is incorporated in an amount effective to enhance theantifog performance of the laminate 10.

Optional Energy Treatment of the Sealant and/or Barrier Films

One or more of the thermoplastic layers of the sealant and/or barrierfilms—or at least a portion of the entire sealant and/or barrierfilms—may be cross-linked to improve the strength of the film, improvethe orientation of the film, and help to avoid burn through during heatseal operations. Cross-linking may be achieved by using chemicaladditives or by subjecting one or more film layers to one or moreenergetic radiation treatments—such as ultraviolet, X-ray, gamma ray,beta ray, and high energy electron beam treatment—to inducecross-linking between molecules of the irradiated material. Usefulradiation dosages include at least about any of the following: 5, 7, 10,15, 20, 25, 30, 35, 40, 45, and 50 kGy (kiloGrey). Useful radiationdosages include less than about any of the following: 130, 120, 110,100, 90, 80, and 70 kGy (kiloGrey). Useful radiation dosages include anyof the following ranges: from 5 to 150, from 10 to 130, from 5 to 100,and from 5 to 75 kGy.

All or a portion of one or two surfaces the sealant film and/or thebarrier film may be corona and/or plasma treated to change the surfaceenergy of the film, for example, to increase the ability to print orlaminate the film. One type of oxidative surface treatment involvesbringing the sealant film into the proximity of an O₂— or N₂-containinggas (e.g., ambient air) which has been ionized. Exemplary techniques aredescribed in, for example, U.S. Pat. No. 4,120,716 (Bonet) and U.S. Pat.No. 4,879,430 (Hoffinan), which are incorporated herein in theirentirety by reference. The sealant film may be treated to have a surfaceenergy of at least about 0.034 J/m², preferably at least about 0.036J/m², more preferably at least about 0.038 J/m², and most preferably atleast about 0.040 J/m².

Manufacture and Orientation of the Sealant and Barrier Films

The sealant film 12 and barrier film 14 may each be separatelymanufactured by thermoplastic film-forming processes known in the art(e.g., tubular or blown-film extrusion, coextrusion, extrusion coating,flat or cast film extrusion). A combination of these processes may alsobe employed.

Each of the sealant film 12 and barrier film 14 may be oriented (i.e.,before lamination discussed below) or non-oriented. Either or both ofthe sealant film 12 and the barrier film 14 may be oriented in eitherthe machine (i.e., longitudinal) or the transverse direction, or in bothdirections (i.e., biaxially oriented), for example, in order to enhancethe optics, strength, and durability of the film. Each of the sealantand barrier films may independently be oriented in at least onedirection by one of the following ratios: at least about 2.5:1, fromabout 2.7:1 to about 10:1, at least about 2.8:1, at least about 2.9:1,at least about 3.0:1, at least about 3.1:1, at least about 3.2:1, atleast about 3.3:1, at least about 3.4:1, at least about 3.5:1, at leastabout 3.6:1, and at least about 3.7:1. If it is desired to reduce theheat shrink attribute of a film to a desired level after the film isoriented, then the film may be heat set or annealed after orientation.

Laminate

Laminate 10 includes sealant film 12 laminated to barrier film 14trapping the printed image 16 between the sealant and barrier films.Inside sealant film 12 and the outside barrier film 14 have free shrinkattributes. The resulting laminate 10 presents a superior appearanceupon sealing to the support member 18 (as described below).

Laminate 10 also has a heat-shrink attribute which may come into effectupon exposure to the elevated temperatures associated with sealing thelaminate 10 to the support member. The laminate 10 may have any of afree shrink in at least one direction (machine or transverse direction),in at least each of two directions (machine and transverse directions),or a total free shrink of at least about any of the following values:10%, 12%, 14%, 16%, 18%, 20%, and 25% when measured at 200° F.; and atleast about 21%, 23%, 25%, 30%, 35%, and 40% when measured at 240° F. Itis believed that heat sealing a laminate to a support member (e.g.,tray) where the laminate has free shrinks of these values at both 200°F. and 240° F. reduces the amount and size of wrinkles and/or waves thatmay otherwise form in the lid of the resulting sealed package.

If laminate 10 has too much heat-shrink attribute for a given supportmember construction, then the laminate may cause support structure 18 tobend, bow, or otherwise distort after exposure to the elevatedtemperatures associated with sealing the laminate 10 to the supportmember. Laminate 10 may have any of a free shrink in at least onedirection (machine or transverse direction), in at least each of twodirections (machine and transverse directions), or a total free shrinkof less than about any of the following values: 70%, 60%, 50%, 40%, and30% when measured at 200° F.; and less than about 90%, 80%, 70%, 60%,and 50% when measured at 240° F.

The thickness of the laminate may be less than about any of thefollowing values: 10, 7, 5, 4, 3, 2.8, 2.5, 2.3, 2.2, 2.1, 2, 1.9, 1.8,and 1.7 mils. The oxygen transmission rate attributes of the laminateare discussed in the Barrier Layer section above.

Trap Printed Image

A printed image 16 is disposed (i.e., trap printed) between the sealantand barrier films at the interface between the outside surface 26 ofsealant film 12 and the inside surface 34 of the barrier film 14. Thismay be accomplished by printing one or more images 16 on one or both ofthese surfaces before laminating the films together, so that uponlamination the printed images 16 are “trapped” between the two films.For example, the printed image may be “reverse trap printed” by printingthe image onto surface 34 of the barrier film.

The trapped print 16 is visible through a relatively transparent barrierfilm to provide information to the retail purchaser of the package.Accordingly, package 10 may be provided with consumer-specificinformation at the time of packaging at a centralized packagingfacility, in the form of a printed image trapped within the laminate 10used at part of the sealed package 20. The availability of trap printedinformation in laminate 10 reduces and potentially eliminates the needfor additional package printing or labeling at the retail distributionpoint. The printed image 16 may include indicia such as productinformation, nutritional information, source identification, and otherinformation, as discussed above. The laminate may include a plurality ofrepeating printed images for each package (i.e., “scatter print”) inwhich registration of the printed laminate 10 with the support member 18is less important—or the printed image may require registration to placethe printed image of the laminate in appropriate alignment with thesupport member 18 before sealing the lidstock to the support member(i.e., “registered print”).

To form the printed image, one or more layers of ink are printed ontothe print surface. The ink is selected to have acceptable ink adhesion,appearance, and heat resistance once printed on the film. The film maybe printed by any suitable method, such as rotary screen, gravure, orflexographic techniques. Inks and processes for printing on plasticfilms are known to those of skill in the art. See, for example, Leach &Pierce, The Printing Ink Manual, (5^(th) ed., Kluwer AcademicPublishers, 1993), which is incorporated herein in its entirety byreference.

To improve the adhesion of the ink to the surface of the sealant orbarrier film, the surface of the sealant or barrier film may be treatedor modified before printing. Surface treatments and modificationsinclude: i) mechanical treatments, such as corona treatment, plasmatreatment, and flame treatment, and ii) primer treatment. Surfacetreatments and modifications are known to those of skill in the art. Theflame treatment is less desirable for a heat-shrinkable film, since heatmay prematurely shrink the film. The ink system should be capable ofwithstanding without diminished performance the temperature ranges towhich it will be exposed during lamination, heat sealing, packaging, andend use.

Appearance Characteristics of the Laminate

Each of laminate 10 and barrier film 14 may have low hazecharacteristics. Haze is a measurement of the transmitted lightscattered more than 2.5° from the axis of the incident light. Haze ismeasured against the outside surface 36 of the barrier film 40,according to the method of ASTM D 1003, which is incorporated herein inits entirety by reference. All references to “haze” values in thisapplication are by this standard. Preferably, the haze of eitherlaminate 10 or barrier film 14 is no more than about (in ascending orderof preference) 20%, 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, and 3%.

Laminate 10 preferably has a gloss, as measured against the outsidesurface 36 of the barrier film 40 of at least about (in ascending orderof preference) 40%, 50%, 60%, 63%, 65%, 70%, 75%, 80%, 85%, 90%, and95%. These percentages represent the ratio of light reflected from thesample to the original amount of light striking the sample at thedesignated angle. All references to “gloss” values in this applicationare in accordance with ASTM D 2457 (45° angle).

Preferably, laminate 10 is transparent (at least in the non-printedregions) so that the packaged food item 22 is visible through thelaminate. “Transparent” as used herein means that the material transmitsincident light with negligible scattering and little absorption,enabling objects (e.g., packaged food or print) to be seen clearlythrough the material under typical unaided viewing conditions (i.e., theexpected use conditions of the material). If laminate 10 is transparentthen both barrier film 14 and sealant film 12 are also transparent.Optionally, barrier film 14 may be transparent while sealant film isopaque, in which case laminate 10 is opaque while trap print 16 is stillclearly visible through barrier film 14. Preferably, the transparency(i.e., clarity) of any of the laminate 10, sealant film 12, and barrierfilm 14 are at least about any of the following values: 65%, 70%, 75%,80%, 85%, and 90%, as measured in accordance with ASTM D1746.

Modulus of the Laminate

Laminate 10 preferably exhibits a Young's modulus sufficient towithstand the expected handling and use conditions. Young's modulus maybe measured in accordance with one or more of the following ASTMprocedures: D882; D5026-95a; D4065-89, each of which is incorporatedherein in its entirety by reference. Each of the sealant film 12,barrier film 14, and/or laminate 10 may have a Young's modulus of atleast about any of the following: 70,000, 80,000, 90,000, 100,000,150,000, 200,000, 250,000, 300,000, 350,000 pounds/square inch, measuredat a temperature of 73° F. A higher modulus film has an enhancedstiffness, which may help reduce the tendency of the trap printed image16 to crack when the laminate is flexed. Further, it is helpful thatbarrier film 12 have a high modulus at the elevated temperatures presentwhen the laminate 10 is exposed to heat seal temperatures, for example,during the lidstock sealing process discussed below. Accordingly, theYoung's modulus of the barrier film 14 may be greater than the modulusof the sealant film 12, for example, greater by at least about one ofthe following amounts: 25%, 30%, 35%, 40%, 45%, 50%, 60%, 70%, 75%, 80%,90%, 100%, 125%, 150%, 175%, 200%, 400%, and 600%.

Manufacture of the Laminate

To manufacture laminate 10, the outside surface 26 of the sealant film12 is placed adjacent to or in contact with the inside surface 34 ofbarrier film 14 so that the films may be bonded together by a suitablelamination technique. Suitable lamination techniques are known in theart, and include adhesive bonding, reactive surface modification (e.g.,corona treatment, flame treatment, or plasma treatment), heat treatment,pressure treatment, heat-welding, and combinations thereof. Suitablelamination methods are described in U.S. Pat. No. 5,779,050 issued Jul.14, 1998 to Kocher et al entitled “Lidded Package Having a Tab toFacilitate Peeling,” which is incorporated herein in its entirety byreference.

Barrier film 14 may be directly laminated to sealant film 12. The term“directly laminated” as used herein means that a first film is bonded toa second film by a suitable lamination method without an additional filmbetween the first and second films. The first film (e.g., sealant film)may be considered as “directly laminated” to the second film (e.g.,barrier film)—even if additional material is present between the firstand second films—if the additional material is present primarily tofacilitate the lamination of the first and second films (e.g., anadhesive used in adhesive lamination) or to form part of the trap print(e.g., a printed image) between the first and second films.

Laminate 10 has an inter-film bond strength sufficient to survive theexpected packaging and end use conditions without delamination. The term“inter-film bond strength” as used herein means the amount of forcerequired to separate or delaminate two directly laminated films, asmeasured in accordance with ASTM F88-94 where the Instron tensile testercrosshead speed is 5 inches per second, using five, 1-inch wide,representative samples. Preferably, the inter-film bond strength betweensealant film 12 and barrier film 14 is at least about any of thefollowing values: 0.5, 0.7, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.7, 2, and2.5 pounds/inch.

As a reactive surface modification lamination method, corona treatmentmay be combined with pressure and, optionally, heat immediately afterthe corona treatment. The corona treatment provides the film with areactively modified surface to enhance lamination bonding. The amount ofcorona discharge to which the films are exposed is directly proportionalto the amount of power supplied to the corona treatment units, and alsoindirectly proportional to the speed at which the films are passedthrough the units. In general, corona treatment units operate by passinga high voltage electrical current through an electrode positionedadjacent a film surface to be treated. The electrode then produces anelectrical discharge which ionizes the surrounding air to cause reactivesurface modification, e.g., oxidation, of the treated film surface.

Any desired combination of power input to the corona unit and film speedmay be employed to achieve a desired bond-strength between the films.The amount of power to supplied to the corona treatment units may range,for example, from about 0.02 to about 0.5 kilowatts (kw) per inch offilm width. The film speed through the corona treatment unit may range,for example, from about 10 to about 2000 feet/minute.

Alternatively or in addition to a reactive surface modificationlamination method, heat-welding may be employed to laminate the filmstogether. For example, skin layer 30 of sealant film 12 and inside layer38 of barrier film 14 may comprise materials capable of forming aheat-weld bond during lamination. Suitable materials for the interfacinglayers for a heat-weld lamination were discussed above in conjunctionwith the sealant layer of the sealant film. The same or differentthermoplastics may be included in the adjacent film layers.

In order to facilitate fast and reliable sealing of the lidstocklaminate 10 to the support member, it is preferable that laminate 10 hasgood hot tack attributes. The term “hot tack” is understood to those ofskill in the art. Preferably, laminate 10 has a hot tack strength of atleast 2 Newtons, more preferably at least about 4 Newtons.

Sealed Package

The lidstock laminate 10 may be heat sealed to support member 18 to formsealed package 20.

Support Member

Support member 18 is a component of package 20 in addition to laminate10. Product 22 (e.g., a food product) may be disposed on or in supportmember 18. For example, meat products may be disposed in a tray-likesupport member comprising, for example, expanded polystyrene sheetmaterial that has been thermoformed into a desired shape for supportingthe meat product. Product support member 18 preferably is in the form ofa tray having side walls 50 and base 52—which define cavity 46 intowhich the product 22 may be disposed. A peripheral flange 48 preferablyextends from side walls 50 to provide a sealing surface for attachmentof lid 10 to the support member 18 to enclose the product 22 within thecavity 46.

Although the drawings show support member 18 in one configuration,support member 18 may have any desired configuration or shape, such asrectangular, round, or oval. The support member may be substantiallyrigid, semi-rigid, or flexible. For example, the support member may havea 1% secant flex modulus of at least about any of the following values:120,000, 140,000, 160,000, 180,000, 200,000, and 225,000 pounds/squareinch.

Flange 48 may also have any desired shape or design, such as thesubstantially flat design presenting a single sealing surface as shownin the drawings, or a more elaborate design which presents two or moresealing surfaces, such as the flange configurations disclosed in U.S.Pat. Nos. 5,348,752 and 5,439,132, the disclosures of which areincorporated herein by reference.

Support member 18 may be formed from any material useful for theexpected end use conditions, including polyvinyl chloride, polyethyleneterephthalate, polystyrene, polyolefins (e.g., high density polyethyleneor polypropylene), paper pulp, nylon, and polyurethane. The supportmember may be foamed or non-foamed as desired. Support member 18 mayhave oxygen transmission barrier attributes, particularly when product22 is an oxygen-sensitive food product. When such oxygen-sensitiveproducts are to be packaged in a modified atmosphere environment toextend either bloom-color life or shelf-life, support member 18preferably has a thickness and composition sufficient to provide anoxygen transmission rate of no more than about any of the followingvalues: 1000, 500, 150, 100, 50, 45, 40, 35, 30, 25, 20, 15, 10, and 5cubic centimeters (at standard temperature and pressure) per squaremeter per day per 1 atmosphere of oxygen pressure differential measuredat 0% relative humidity and 23° C.

To achieve oxygen barrier attributes, support member 18 may comprise oneor more of the barrier components discussed above in the Barrier Layersection in order to provide oxygen barrier attributes to the supportmember. Such barrier components may be incorporated within structuralsections or aspects of the support member—or optionally incorporated ina surface layer or film 54 laminated or otherwise bonded to form theinside surface of the support member, as described in U.S. Pat. Nos.4,847,148 and 4,935,089, and in U.S. Ser. No. 08/326,176, filed Oct. 19,1994 and entitled “Film/Substrate Composite Material” (published as EP707 955 A1 on Apr. 24, 1996), each of which is incorporated herein inits entirety by reference.

In addition to (or as an alternative to) providing oxygen barrierattributes, the surface layer or film 54 may enhance the sealability ofthe lidstock laminate 10 to the support member 18. In heat sealinglaminate 10 to the support member 18, layer or film 54 of the supportmember contacts and melds with sealant layer 28 of the sealant film 12to form heat seal 44. To facilitate a strong heat seal 44, layer or film54 may comprise one or more thermoplastics that are compatible with thethermoplastic composition of the sealant layer 28. Accordingly, layer orfilm 54 may comprise any of the polymer compositions and thicknesses asdiscussed in the Sealant Layer and Skin Layer sections regarding sealantfilm 12. The outer surface of layer or film 54 may comprise polymerhaving a melting point or softening point essentially equivalent to orless than that of the polymer forming surface 24 of sealing layer 28,for example, less by about any of the following values: 5° F., 10° F.,15° F., 20° F.

It was discovered that a strong bond between the laminate 10 and supportmember 18 may be formed where the melting point of the polymer formingthe surface of layer 54 is higher than the melting point of the polymerforming the surface 24 of sealant layer 28—for example, a bond strongerthan that formed where the melting point of the polymer forming thesurface of layer 54 was lower than the melting point of the polymerforming the surface of sealant layer 28.

It is believed that the result of the stronger bond with a relativelyhigher melting point surface layer 54 was facilitated where themelt-flow index of the surface layer 54 was lower than the melt-flowindex of the sealant layer 28 of the sealant film. Accordingly, themelt-flow index of the polymer forming surface layer 54 may be lowerthan the melt-flow index of the polymer forming the surface 24 ofsealant layer 28, for example lower by at least about any of thefollowing values: 0.2, 0.5, 0.7, 1, 1.4, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3,3.5, and 4 g/10 minutes.

As previously discussed, the sealant layer 28 may comprise one or morepolymers. There is inherently a highest temperature above which themelting point or softening point of at least 70 weight % of the one ormore polymers of the sealant layer exists. Similarly, there are suchhighest temperatures for other such selected weight percentages, such as80, 90, and 100%. The sealing area of the outer surface of the supportmember or layer 54 may comprise any of at least about 70, 80, 90, or 100weight % of one or more polymers each having a melting point orsoftening point at least about any of 3° F., 5° F., 7° F., 10° F., 15°F., 30° F., or 35° F. higher than such highest temperature.

Manufacture of the Sealed Package

To make sealed package 20, the item to be packaged (e.g., product 22)may be placed onto support member 18. Then laminate 10 is placed overthe support member so that the sealant film 12 of the laminate contactsthe support member 18. Laminate 10 may be supplied from a larger web ofthe laminate, for example, from a roll that is unwound to supplylaminate as needed.

A heated bar or member engages the perimeter of the lid 10 correspondingwith the perimeter flange 48 of the support member to compress the lidagainst the flange of the support member. The resulting heat transferand compression causes the sealant layer 28 of the lid and surface layer54 of the support member to soften and intermix with one another. Theheat from the sealing operation may also initiate shrinking of the heatshrinkable laminate to reduce the amount of wrinkles or waves that mayotherwise form in the lid. The excess lid material extending beyond theflange may be trimmed by a cutting operation. Further, if the laminateis supplied from a roll, portions may be severed from the web after orsimultaneously with the heat-welding of the laminate to support member18. Laminate 10 may be severed by a conventional cutting device (e.g., asharp cutting instrument or a thermal cutting device such as a heatedwire or heated blade). The heating bar is removed to allow the sealedarea to cool and form a sealed bond. A representative process for heatsealing a lid to a support member is described in U.S. Pat. No.5,779,050 to Kocher, which was previously incorporated by reference.

The resulting heat-weld or heat-seal 44 preferably extends continuouslyaround the upper surface of flange 48 to hermetically seal or encloseproduct 22 within package 20. In this manner, laminate 10 and supportmember 18 preferably form a substantially gas-impermeable enclosure forproduct 22 to protect it from contact with the surrounding environmentincluding, atmospheric oxygen, dirt, dust, moisture, liquid, andmicrobial contaminates. Product 22 may be packaged in a modifiedatmosphere where product 22 is oxygen-sensitive (i.e., perishable,degradable, or otherwise changeable in the presence of oxygen) in orderto extend the shelf life or bloom-color life. Such oxygen-sensitiveproducts include fresh red meat products (e.g., beef, veal, lamb, andpork), poultry, fish, and cheese.

The sealing of the laminate 10 to support member 18 may be by one ormore of the heat sealing methods, including thermal conductance sealing(as described above), impulse sealing, ultrasonic sealing, anddielectric sealing.

Product 22 is shown as a “low profile” product—that is, a product havinga maximum height that is below the maximum height of support member 18(i.e., the level at which flange 48 is located). However, a “highprofile” product—that is, a product having a maximum height that isabove the maximum height of support member 18—may also be packaged inaccordance with the present invention so that the portion of the productwhich extends above the level of flange 48 will be in contact with lid10.

Seal Strength

The resulting heat seal bond 44 between the laminate 10 and the support18 is sufficiently strong to withstand the expected use conditions. Forexample, the heat seal bond strength may be at least about any of thefollowing values: 0.5, 0.6, 0.7, 0.8, 0.9. 1, 1.3, 1.5, 1.8, 2, 2.5, 3,3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, and 8 pound/inch. The term “heatseal bond strength” as used herein means the amount of force required toseparate the sealant layer of the laminate from the support member towhich the sealant layer has been sealed, as measured in accordance withASTM F88-94 where the Instron tensile tester crosshead speed is 5 inchesper second, using five, 1-inch wide, representative samples.

Preferably, the weakest point of any of the inter-layer bond strength ofthe sealant film, the inter-layer bond strength of the barrier film, theintra-layer cohesive strength of the layers of the sealant and barrierfilms, and the inter-film bond strength is located from the insidesurface 24 of the sealant film by a distance of at least about any ofthe following values: 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2 mils.

Further, the resulting sealed packaged also has a seal strengthsufficient to withstand the expected end use conditions, for example, aseal strength of at least about any of the following values: 3, 3.5, 4,4.5, 5, 5.5, 6, 6.5, 7, and 7.5 pounds/inch. The term “seal strength” inconjunction with a sealed package refers to the maximum amount of forcerequired to cause a cohesive or adhesive failure either within laminatethat is sealed to the support member, in the bond between the laminateand the support member of the package, or in the support member itself,measured in accordance with ASTM F88-94 by pulling representativesamples of the film or laminate sealed to the support member using anInstron tensile tester with a crosshead speed of 5 inches per second andaveraging the results from five, 1-inch wide, representative samples.ASTM F88-94 is incorporated herein in its entirety by reference.

As used herein, an “adhesive failure” is a failure in which theinterfacial forces (e.g., valence forces or interlocking action or both)holding two surfaces together are overcome. A “cohesive failure” is onein which the molecular attractive forces holding together a layercomposition are overcome.

Preferably, each of the sealed package 20, laminate 10, and the filmsincorporated in laminate 10 (e.g., sealant film 12 and barrier film 14)are non-peelable. The term “non-peelable” used in conjunction with asealed package, laminate, or film means that the seal strength failuremode results in a jagged, tattered, or ragged separation—that is, onethat does not cleanly, consistently, or reliably fail in the same mannerand along the same position each time. In this sense, the seal strengthfailure mode of a non-peelable film or laminate is contrary to that of apeelable film, which is specifically designed to fail cleanly,consistently, and reliably in the same manner and along the samerelative position each time, for example by incorporation ofnon-compatible thermoplastics and/or contaminates in two adjacent filmlayers to facilitate peeling and also by incorporating a mechanism suchas a tab to initiate a peel separation, as described in U.S. Pat. No.5,919,547 issued Jul. 6, 1999 to Kocher entitled “Laminate Having aCoextruded, Multilayer Film Which Delaminates and Package MadeTherefrom,” which is incorporated herein in its entirety by reference.

The following examples are presented for the purpose of furtherillustrating and explaining the present invention and are not to betaken as limiting in any regard.

EXAMPLES

In the comparatives and examples below, the following materials wereused:

“Additives” are 5% antifog additives and 2% antiblock additives;

“Adhesive 1” is a methylene bis(phenyl isocyanate), an ethyl ester ofacetic acid and a polyol curing agent;

“EPC” is a propylene-ethylene copolymer with 3.3% ethylene content and amelting point of 139° C. available from ExxonMobil under the trademarkEscorene PD9302;

“EVOH1” is an ethylene/vinyl alcohol copolymer having 44 mole % ethylenecontent, a melt flow index of 1.6, and a melting point of 165° C.;

“ION” is an ionomer resin modified with nylon available from DuPontCorporation under the trademark SURLYN AM 7927;

“LLDPE1” is a heterogeneous ethylene/octene copolymer having a melt-flowindex of 1.0 and a density of 0.920 g/cc, available from the DowChemical Company (Midland, Mich.) under the DOWLEX 2045 trademark;

“LMDPE” is a heterogeneous ethylene/octene copolymer having an octenecontent of 2.5 weight %, a melt-flow index of 2.5, and a density of0.935 g/cc, available from the Dow Chemical Company (Midland, Mich.)under the DOWLEX 2037 trademark;

“MB” is a masterbatch of 90.3% polypropylene homopolymer (ESCORENEPD4062 available from ExxonMobil), 4% inorganic antiblock, and 5.7% slipand antiblock agents;

“MPE” is a homogeneous ethylene/hexene/butene terpolymer having a meltflow index of 2.0 and a density of 0.902 g/cc, available from ExxonMobilCorporation under the EXACT 9103 trademark;

“Nylon1” is a nylon 6/66 copolymer having a melting point of 196° C.;

“Nylon2” is a nylon 6/12 copolymer having a melting point of 130° C.;and

“Tie 1” is an anhydride-grafted LLDPE.

Example 1

A trap-printed laminate having the composition and construction shown inTable 1 was formed by adhesively laminating a First Film (i.e., shrinksealant film) to a Second Film (i.e., shrink barrier film) having aprinted image on its inside surface. The Example 1 laminate had a totalthickness of 1.85 mils. The films used to form the Example 1 laminateand the resulting Example 1 laminate itself had the free shrinks asreported in Table 2. The sealant layer side of the Example 1 laminatewas heat sealed to a plastic tray (commercially available from CryovacInc. under the tradename CS977) to form a sealed package. The lid of theresulting package was free from visible wrinkles, film corrugations, andwaves to present a tight, wrinkle-free appearance.

TABLE 1 Thickness Film Layer Designation Layer Composition of LayerDesignation (Function) (weight %) (mils) First Film First 93% MPE; 0.2(inside or sealant layer)  7% Additives Second 70% LLDPE1; 0.2 23%LMDPE;  7% Additives Third 50% LLDPE1; 0.5 50% LMDPE Fourth (outside,skin) 70% LLDPE1; 0.1 23% LMDPE;  7% Additives Lamination adhesiveAdhesive1 0.1 Second Film First (skin layer) 95% EPC; 0.2  5% MB Second(tie) Tie1 0.07 Third 80% Nylon1 0.07 (bulk, barrier protection) 20% IONFourth (barrier) 90% EVOH1 0.07 10% Nylon2 Fifth 80% Nylon1 0.07 (bulk,barrier protection) 20% ION Sixth (tie) Tie1 0.07 Seventh (skin layer)95% EPC; 0.2  5% MB

TABLE 2 Shrink (%) Direction of Example 1 Comparative 1 Film/LaminateShrink 200° F. 240° F. 200° F. 240° F. 1^(st) (sealant) Machine 9 48 948 Transverse 18 53 18 53 2^(nd) (barrier) Machine 16 31 5 16 Transverse17 34 3 13 Laminate Machine 11 30 8 17 Transverse 16 35 9 20 ShrinkRatio Machine 1.78 0.65 0.56 0.33 of 2^(nd) Film to Transverse 0.94 0.640.17 0.25 1^(st) Film

Comparative 1

A trap-printed laminate having the composition and construction shown inTable 3 was formed by adhesively laminating a First Film (i.e., the samefilm as used in Example 1) to a Second Film having a printed image onits inside surface. The Second Film is a biaxially oriented three-layercoextrusion commercially available from Unitika Ltd. (Osaka, Japan)under the EMBLON E801-15 trademark. The Second Film is 0.6 mils thickand is believed to comprise about 66% nylon and 34% ethylene/vinylalcohol copolymer, as represented in Table 3. The Comparative 1 laminatehad a total thickness of about 1.7 mils. The films used to form theComparative 1 laminate and the resulting laminate had the free shrinksas reported in Table 2. The sealant layer side of the Comparative 1laminate was heat sealed to the same tray as described above for Example1 under the same sealing conditions as Example 1 to form a sealedpackage. The lid of the resulting Comparative package had waves andwrinkles in the form of film corrugations along the sealing edge of thelid at the leading and trailing edges of the package.

TABLE 3 Thickness Film Layer Designation Layer Composition of LayerDesignation (Function) (weight %) (mils) First Film First 93% MPE; 0.2(inside or sealant layer)  7% Additives Second 70% LLDPE1; 0.2 23%LMDPE;  7% Additives Third 50% LLDPE1; 0.5 50% LMDPE Fourth (outside,skin) 70% LLDPE1; 0.1 23% LMDPE;  7% Additives Lamination adhesiveAdhesive1 0.1 Second Film First (skin layer) polyamide (nylon) Second(barrier) ethylene vinyl alcohol Third (skin layer) polyamide (nylon)

The above descriptions are those of preferred embodiments of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theclaims, which are to be interpreted in accordance with the principles ofpatent law, including the doctrine of equivalents. All parts andpercentages are by weight, unless otherwise indicated or well understoodin the art. Except in the claims and the specific examples, or whereotherwise expressly indicated, all numerical quantities in thisdescription indicating amounts of material, reaction conditions, useconditions, molecular weights, and/or number of carbon atoms, and thelike, are to be understood as modified by the word “about” in describingthe broadest scope of the invention. Any reference to an item in thedisclosure or to an element in the claim in the singular using thearticles “a,” “an,” “the,” or “said” is not to be construed as limitingthe item or element to the singular unless expressly so stated. Allreferences to ASTM tests are to the most recent, currently approved, andpublished version of the ASTM test identified, as of the priority filingdate of this application. Each such published ASTM test method isincorporated herein in its entirety by reference.

What is claimed is:
 1. A method of forming a package comprising: a)providing a laminate comprising: a first film having an inside surfaceand an outside surface opposite the inside surface of the first film,the first film comprising a sealant layer forming the inside surface ofthe first film, the sealant layer comprising one or more polymers eachhaving a given melting point, whereby at least one polymer of thesealant layer has the lowest melting point of the one or more polymersin the sealant layer; a second film having an inside surface and anoutside surface opposite the inside surface, the second film comprisingan outside layer forming the outside surface of the second film, theoutside layer comprising at least about 40% by weight of the outsidelayer of one or more relatively high-melt polymers each having a meltingpoint at least about 25° F. higher than the lowest melting point polymerof the sealant layer; and a printed image between the first and secondfilms, wherein: the first film has an oxygen transmission rate greaterthan the oxygen transmission rate of the second film, measured (atstandard temperature and pressure) per square meter per day per 1atmosphere of oxygen pressure differential measured at 0% relativehumidity and 23° C.; the laminate has an oxygen transmission rate of nomore than about 100 cubic centimeters (at standard temperature andpressure) per square meter per day per 1 atmosphere of oxygen pressuredifferential measured at 0% relative humidity and 23°C.; the laminatehas a free shrink in each of the transverse and machine directions of atleast about 10% at 200° F. and at least about 21% at 240° F.; and b)heat sealing the laminate to a support member to form a closed packages,wherein the inside surface of the first film is adjacent the interior ofthe closed package.
 2. The method of claim 1 wherein the providedlaminate has a free shrink in the transverse direction of at least about12% at 200° F. and at least about 23% at 240° F.
 3. The method of claim1 wherein the provided laminate has a free shrink in the transversedirection of at least about 14% at 200° F. and at least about 25% at240° F.
 4. The method of claim 1 wherein the provided laminate has afree shrink in the transverse direction of at least about 16% at 200° F.and at least about 30% at 240° F.
 5. The method of claim 1 wherein theprovided laminate has a free shrink in the machine direction of at leastabout 11% at 200° F. and at least about 30% at 240° F. and a free shrinkin the transverse direction of at least about 16% at 200° F. and atleast 35% at 240° F.
 6. The method of claim 1 wherein the free shrinkvalues of the second film of the provided laminate measured at each of200° F. and 240° F. in each of the machine and transverse directions arefrom about 0.3 to about 3 times the free shrink values of the first filmof the provided laminate measured at the corresponding temperature anddirection.
 7. The method of claim 1 wherein the free shrink values ofthe second film of the provided laminate measured at each of 200° F. and240° F. in each of the machine and transverse directions are from about0.5 to about 3 times the free shrink values of the first film of theprovided laminate measured at the corresponding temperature anddirection.
 8. The method of claim 1 wherein the free shrink values ofthe second film of the provided laminate measured at each of 200° F. and240° F. in each of the machine and transverse directions are from about0.6 to about 2.5 times the free shrink values of the first film of theprovided laminate measured at the corresponding temperature anddirection.
 9. The method of claim 1 wherein the free shrink values ofthe second film of the provided laminate measured at each of 200° F. and240° F. in each of the machine and transverse directions are from about0.6 to about 2 times the free shrink values of the first film of theprovided laminate measured at the corresponding temperature anddirection.
 10. A package formed by the method of claim
 1. 11. The methodof claim 1 wherein the outside layer comprises at least about 60% byweight of the outside layer of the one or more relatively high-meltpolymers.
 12. The method of claim 1 further comprising placing a foodproduct on the support member before heat sealing the laminate to thesupport member to enclose the food product in the package.
 13. Themethod of claim 1 wherein the laminate has an oxygen transmission rateof no more than about 50 cubic centimeters (at standard temperature andpressure) per square meter per day per 1 atmosphere of oxygen pressuredifferential measured at 0% relative humidity and 23° C.
 14. The methodof claim 1 wherein the sealant layer comprises at least 30% based on theweight of the sealant layer of a polymer having a melting point of lessthan about 115° C.
 15. The method of claim 1 wherein the first film isun-perforated.
 16. The method of claim 1 wherein the second film has anoxygen transmission rate of no more than about 30 cubic centimeters (atstandard temperature and pressure) per square meter per day per 1atmosphere of oxygen pressure differential measured at 0% relativehumidity and 23° C.
 17. The method of claim 1 wherein the image isprinted on the inside surface of the second film.
 18. The method ofclaim 1 wherein the second film has a Young's modulus of at least about150,000 pounds/square inch.
 19. The method of claim 1 wherein thethickness of the first film is greater than or equal to the thickness ofthe second film.
 20. The method of claim 1 wherein each inter-layer bondstrength of the first film of the provided laminate is at least 2.5pound/inch.
 21. The method of claim 1 wherein the closed package has aseal strength of at least about 5 pounds/inch.
 22. The method of claim 1wherein the closed package has a seal strength of at least about 6pounds/inch.
 23. The method of claim 1 wherein the provided laminate isnon-peelable.
 24. The method of claim 1 wherein the sealant film of theprovided laminate is non-peelable.
 25. The method of claim 1 wherein thesupport member comprises a rigid tray.
 26. The method of claim 1 whereinthe sealant layer of the first film of the provided laminate comprisesone or more polymers, whereby there is a highest temperature above whichthe melting point of at least 70 weight % of the one or more polymers ofthe sealant layer exists; and the support member comprises a sealingarea to which the laminate is sealed, the sealing area of the supportmember comprising at least about 70 weight % of one or more polymerseach having a melting point at least about 3° F. higher than saidhighest temperature.
 27. The method of claim 26 wherein the at leastabout 70 weight % of one or more polymers of the sealing area each has amelting point at least about 7° F. higher than said highest temperature.28. The method of claim 1 wherein sealing the laminate to the supportmember encloses within the package interior oxygen concentrationdifferent from that of ambient air.